The present invention relates to an electrical connector organizer and printed circuit board stiffener. More particularly, the present invention relates to a connector organizer and board stiffener that permits use of two piece modular connector assembly without using valuable printed circuit board real estate.
The current industry standard for a two part modular connector system for electrically coupling a backplane to a daughtercard is set in the United States by specification EIA/IS-64 from Electronic Industries Association. This specification sets out parameters for 2 mm, two-part connectors for use printed with circuit boards and backplanes. The international standard for such two-part connectors is set forth in IEC 1076-4-001 specification 48B.38.1. Both of these specifications define a daughtercard connector (free board connector) that includes female receptacle contacts and a backplane or motherboard connector (fixed board connector) that contains male pin contacts. A connector that contains female receptacle contacts is commonly referred to as a "socket" connector, and a connector that contains male pin contacts is commonly referred to as a "header" connector.
The present invention relates to a high density backplane interconnect system that incorporates a printed circuit board ("PCB") support structure. This PCB support structure (hereinafter referred to as a "board stiffener") is considered necessary to prevent bow or misalignment problems that often arise with very long PCB edge style connectors. These alignment problems are most often the result of differences in component thermal expansions. When heated during the soldering phase, the thermoplastic housing material of the connector usually expands at a higher rate that the PCB. The PCB is made from a composite of fiberglass/epoxy resin plus copper traces with plated through holes or pads. Due to built in residual stresses that accumulate during manufacture and assembly of both PCBs and connectors and are subsequently "released" with the application of heat, the components often do not return to their initial alignments after cooling. The relatively rigid metallic contact leads extending from the connector housing are mechanically attached to a pad or a plated through hole on the PCB during the solder phase, then become highly stressed as they are forced to compensate for a misalignment between the PCB and the connector. Being more rigid than the PCB (usually), the thermoplastic housing body of the connector effectively forces the PCB to conform to its new position via the "pull" effect it generates through the contact leads, causing PCB to bow and/or warp. On longer connectors these alignment differences are even more magnified and cause greater problems. For some high end applications, the overall connector length can be well over 10 inches long. Accordingly, the industry often insists on a board stiffener alongside the connector to reduce these undesirable effects.
Traditional board stiffeners consist of a metallic shell or U-shaped bar that is bolted or screwed down to the PCB. In other instances, the board stiffener is also physically attached to the connector. Such board stiffeners are usually made from a metallic material. Because of the much stronger stiffness of the metallic stiffener material compared to the plastic housing or PCB, the stiffener greatly reduces the warp or bow effects between the components. Some problems exist with conventional board stiffeners. These problems include increased board real estate requirements (a major problem in high density packaging applications), and increased assembly costs.
Additionally, on high end backplane systems that require large PCB's and high density motherboard--daughtercard connectors, there is a customer desire for a one housing "long" edge connector solution to facilitate inventory and assembly. However, from a connector supplier's perspective, the manufacture of high density very long connectors is extremely difficult and costly. Due to increased plastic shrinkage effects and very demanding mold flow requirements, the tooling costs to make large quantities of high precision "long and flat" plastic parts as required for microelectronic connector applications, becomes very expensive. Given that different potential customers have different quantities of signal I/O connector requirements, the cost of tooling dedicated high density "long and flat" connectors for each customer application becomes prohibitive.
In an effort to address varying customer applications with a coherent, single connector interface approach, most backplane two-piece connector manufacturers have developed "modular", end-to-end stackable designs. These modular end-to-end stackable designs allowed customers to mix and match several different sized modules to fit their particular application. See, for example, the IEC 48B.38.1 specification discussed above.
The development of the subject invention was undertaken to provide a connector organizer and board stiffener for high density motherboard--daughtercard style applications with a single piece (two pieces total for a mated set) "long and flat" connector. The IEC refers to a motherboard or backplane as a "fixed board" and a daughtercard as a "free board". In addition, the present invention provides a board stiffener that does not increase PCB board real estate requirements or increase customer's component-to-PCB assembly costs. The present invention also provides a system that addresses the one-piece customer requirement and permits use of a modular end-to-end stackable flexible connector system approach.
The connector organizer and board stiffener of the present invention includes a L-shaped metallic strip with openings designed to produce an interference fit with locating pegs extending from underneath the housing body of a thermoplastic connector housing. This connector housing system, explicitly designed for modularity with end-to-end stackability has these locating pegs located in a repeating pattern that correspond to the end-to-end stacking modularity of the connector. The openings on the board stiffener are also repeating and spaced apart a set distance that corresponds to the end-to-end modular stacking distance of the connector system. This configuration allows for different modules to be assembled together on the strip, side by side, and held together and handled as one "assembly". This one-piece assembly can then be easily fitted flush to the surface of a PCB having an edge which has been trimmed by an amount equal to the thickness of the L-shaped strip. Connectors can then be fastened to the PCB in a traditional manner, without any additional assembly step required by the customer to apply a board stiffener. The edge trimming operation of the PCB can be easily accommodated during PCB manufacture.
The apparatus of the present invention permits the connector manufacturer the flexibility to assemble a multitude of connector configurations, supplying his customers a "one-piece solution", yet it eliminates the need to develop dedicated, expensive tooling. In addition, the apparatus serves the dual purpose of reinforcing the strength of the PCB, greatly reducing the potential of bow or warpage, and in effect acting as a board stiffener. By virtue of being underneath the connector, the apparatus of the present invention requires no additional PCB real estate that otherwise could have been allocated to IC logic circuitry. Conventional connector organizers and/or board stiffeners require individual assembly and take up valuable board real estate behind the connector.
The closer that IC circuitry can be placed to the edge of a PCB in a backplane system, the shorter the signal propagation delay on the system. This is a very important criteria for high-speed systems. The apparatus of the present invention advantageously provides improved electrical performance, low applied costs, maximum flexibility and compatibility with a modular design, board reinforcement, and inexpensive manufacturing.
According to one aspect of the present invention, an apparatus is configured to be positioned between an electrical connector and a printed circuit board to strengthen the printed circuit board. The electrical connector has at least one location peg extending therefrom for aligning the electrical connector relative to the printed circuit board. The apparatus includes a generally L-shaped body member having a first leg configured to abut an end edge of the printed circuit board and a second leg configured to abut a surface of the printed circuit board adjacent the end edge. The second leg is formed to include at least one aperture for receiving the at least one location peg of the electrical connector therein to couple electrical connector to the body member.
In the illustrated embodiment, the printed circuit board is formed to include a notched portion adjacent the end edge. The second leg of the L-shaped body member is configured to lie within the notched portion.
The electrical connector includes at least one fixing stud for securing the connector to the printed circuit board. The second leg is formed to include at least one fixing stud aperture to permit the at least one fixing stud to pass through the body member to secure the electrical connector and the body member to the printed circuit board.
According to another aspect of the present invention, an apparatus is configured to be positioned between an electrical connector and a printed circuit board to strengthen the printed circuit board. The printed circuit board has a top surface and is formed to include a notched portion having predetermined depth below the top surface. The electrical connector has at least one location peg extending therefrom to align the connector relative the printed circuit board. The apparatus includes a body member having a thickness substantially equal to the predetermined depth. The body member is configured to be positioned in the notched portion so that a top surface of the body member is substantially coplanar with the top surface of the printed circuit board. The body member is also formed to include at least one aperture for receiving the at least one location peg of an electrical connector therein.
According to yet another aspect of the present invention, an apparatus is provided for organizing a plurality of modular electrical connectors for attachment to a printed circuit board. The plurality of electrical connectors each have at least one fixing stud for securing the connectors to the printed circuit board and at least one location peg to align the electrical connectors relative the printed circuit board. The apparatus includes a body member formed to include a first set of apertures sized to permit the fixing studs to pass therethrough to secure the electrical connector and the body member to the printed circuit board and a second set of apertures configured to engage the location pegs to couple the connectors to the body member. The first and second sets of apertures are arranged in a predetermined pattern to permit a plurality of modular electrical connectors to be mounted end-to-end on the body member prior to coupling the modular electrical connectors and the body member to the printed circuit board.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.